1. Field of the Invention
The present invention relates generally to the field of hazardous waste containment and disposal. In particular, the invention relates to a method and structure suitable for both short and long term storage and permanent disposal of hazardous wastes, particularly nuclear wastes, where the containment structure resists failure from earth movement and allows rapid location and isolation of any leaks which should occur.
Hazardous wastes include a variety of toxic and radioactive substances which would cause harm if released directly into the environment. The various types of hazardous wastes are generally defined by the United States Environmental Protection Agency (EPA) and the Nuclear Regulatory Commission (NRC). With respect to hazardous wastes of a radioactive nature, the NRC presently identifies the following classes of low level wastes with respect to containment and disposal. Class A: Wastes for which there are no stability requirements but which must be disposed of in a segregated manner from other wastes. These wastes, termed class "A", or "segregated wastes, are defined in terms of maximum allowable concentrations of certain isotopes and certain minimum requirements on waste form and packaging that are necessary for safe handling. Class B: Wastes which need to be placed in a stable form and disposed of in a segregated manner from unstable waste forms. These wastes, termed class "B", or "stable" wastes, are also defined in terms of allowable concentrations of isotopes and requirements for a stable waste form as well as minimum handling requirements. Class C: Wastes which need to be placed in a stable form, disposed of in a segregated manner from nonstable waste forms, and disposed of in such a manner that a barrier is provided against potential inadvertent intrusion after institutional controls have lapsed. These wastes are termed class "C", or "intruder protected" wastes, and are also defined in terms of allowable concentrations of isotopes and requirements for disposal by deeper burial or some other barrier.
A fourth class of wastes (mixed wastes) which is not included in the NRC's current listing comprises radioactive wastes contaminated by chemical components classified as hazardous wastes by the EPA.
In general, hazardous wastes cannot be completely eliminated, but rather must be contained in a manner which prevents their release into the environment for very long periods of time, which in practical terms would be considered permanent. A variety of approaches have been proposed for such long term containment, including burial of primary containers holding the waste, disposal of such containers at sea, incorporation of the waste and/or containers of the waste in a solid matrix, such as cement, and the like.
In general, most of the proposed approaches suffer from certain drawbacks. The disposal of wastes in primary containers, such as barrels or drums, either by burial or at sea, depends on the integrity of the container. Encapsulation of the containers in concrete, in contrast, would appear to provide long term stability and containment, but in fact can be subject to failure from a variety of causes, particularly earth movement resulting from earthquakes, earth subsidence and the like. Such earth movements frequently can fracture even the most solid containment matrixes over a long period of time.
An additional problem relates to the detection of leaks in a long term containmnent facility. Although a number of leak detection systems have been proposed, generally they do not allow for precise location of the leak. As many of these containment facilities are quite large, knowledge that a leak has occurred without knowing the precise origin of the leak can be problematic. Moreover, even after the leaks are detected, most storage facilities do not provide for any convenient manner for the leak to be cleaned and facility restored.
For the above reasons, it would be desirable to provide a method and structure for the secure containment of radioactive and other hazardous wastes for very long time periods. In addition, it would be desirable to provide methods and systems for leak detection in such containment structures which would allow the immediate location and isolation of leaks which might occur in the structure, and further allow for correction of the leak and restoration of the structure.
2. Description of the Background Art
The use of nested containers for the storage of nuclear and hazardous wastes has been proposed. See, e.g., U.S. Pat. No. 4,229,316 which describes the use of an inner metal container for storing liquid wastes, where the container is housed in an outer concrete receptacle, and excess space within the receptacle is filled with a radiation-absorptive substance; U.S. Pat. No. 4,588,088 which describes an inner container, typically a metal drum, housed within an exterior container 20, where the interstitial space between the two containers is filled with a sealant material; U.S. Pat. No. 4,453,857, which discloses the sealing of a plurality of containers, typically steel drums, in a solid concrete block; and U.S. Pat. No. 4,513,205, which discloses the use of nested concrete vaults to hold a plurality of inner containers, typically metal barrels. Monitoring of possible leakage of nuclear and hazardous wastes from underground storage systems is known. See, e.g., U.S. Pat. No. 4,513,205, where an inner vault is placed within an observation vault to allow for monitoring of leakage; U.S. Pat. No. 4,464,081, where an underlying pipe and manifold system is placed beneath an underground storage facility to collect seepage and monitor for hazardous wastes; and U.S. Pat. Nos. 4,624,604 and 4,543,031, both of which disclose a leakage detection system located beneath a landfill site. U.S. Pat. No. 4,362,434 discloses a lined basin for the collection of hazardous wastes in bulk. Monitoring of leakage can be done through a sump system. U.S. Pat. No. 4,375,930 also discloses a hazardous waste site having a sump which allows observation of leakage and leachate. U.S. Pat. No. 4,428,700, describes a particular filler which can be used for sealing hazardous waste, either in containers or otherwise, in underground storage locations.